The present invention relates to a stored gas inflator which has a pressure vessel filled with high-pressure gas to eject the gas through a gas port, and more particularly, to a stored gas inflator comprising a burst shim for closing the gas port, and an initiator for applying burst pressure to the burst shim, wherein the burst shim is ruptured by the burst pressure from the initiator to open the gas port.
One known form of a gas supply unit for inflation of an airbag is a stored gas inflator which releases pressurized gas stored in a pressure vessel through a gas port. It should be noted that such an airbag is a safety device mounted in a vehicle such as an automobile and designed to be inflated to protect an occupant in the event of an emergency.
FIG. 4 is a sectional view showing a conventional example of such a stored gas inflator. The stored gas inflator 100 shown in FIG. 4 comprises a pressure vessel 102 which is filled with high-pressure gas. The pressure vessel 102 is provided with gas ports 104 for allowing the high-pressure gas filled therein to be released. Normally, the gas ports 104 are air-tightly closed by a thin-plate-like burst shim 106 which is disposed to overlay an inner surface of the pressure vessel 102. The burst shim 106 is ruptured to open the gas ports 104 when a predetermined pressure (burst pressure) is applied from the outside of the pressure vessel 102.
Near the gas ports 104 of the pressure vessel 102, an initiator (detonator) 108 for applying burst pressure to the burst shim 106 is disposed. The initiator 108 has a base portion 108a fixed to the outer surface of the pressure vessel 102, and a detonating portion 108b extending from the tip of the base portion 108a. The detonating portion 108b explodes in response to a detonation signal from a controller (not shown).
The pressure vessel 102 is provided, near the gas ports 104 thereof, with a burst pressure inlet 110 into which the detonating portion 108b is inserted. The aforementioned burst shim 106 also air-tightly closes the burst pressure inlet 110.
As the initiator 108 receives a detonation signal from the controller (not shown), the detonating portion 108b explodes in the burst pressure inlet 110 so as to apply burst pressure to the burst shim 106 facing the burst pressure inlet 110. As a result, the burst shim 106 is ruptured so as to open the gas ports 104, whereby the gas is released through the gas ports 104.
In the stored gas inflator 100 having the aforementioned structure, the burst shim 106 closing the gas ports 104 is always subjected to the stored gas pressure from the inside of the pressure vessel 102. On the other hand, the initiator 108 applies the burst pressure to the burst shim 106 from the outside of the pressure vessel 102 under a condition at a pressure (atmospheric pressure) significantly lower than the aforementioned stored gas pressure.
Therefore, to rupture the burst shim 106 against the stored gas pressure from the inside of the pressure vessel 102, the initiator 108 must apply burst pressure which is higher twice or more than the stored gas pressure of the pressure vessel 102, so that the required power (explosion power) of the initiator 108 should be extremely high.
It is an object of the present invention to provide a stored gas inflator which is triggered for gas releasing operation even with a relatively low power initiator.
Further objects and advantages of the invention will be apparent from the following description of the invention.
A stored gas inflator of the present invention comprises: a pressure vessel filled with high-pressure gas and having a gas port, a burst shim for closing the gas port; and a gas blasting initiator for applying burst pressure to the burst shim. The pressure vessel is divided into a small chamber facing the gas port and a main chamber having a capacity larger than that of the small chamber. The burst shim is composed of a first burst shim, and a second burst shim, wherein the small chamber and the gas port are partitioned from each other by the first burst shim, and the small chamber and the main chamber are partitioned from each other by the second burst shim. The small chamber and the main chamber are filled with high pressure gas, respectively, and the initiator is mounted to the small chamber. The burst pressure of the second burst shim is set to be lower than the stored gas pressure of the main chamber.
According to the stored gas inflator as mentioned above, the initiator explodes inside the small chamber filled with the high-pressure gas. The first burst shim closing the gas port is always subjected to the stored gas pressure from the inside of the small chamber. As the initiator explodes inside the small chamber, gas blasted by the initiator rapidly increases the inner pressure of the small chamber. When the inner pressure of the small chamber reaches the burst pressure of the first burst shim, the first burst shim is ruptured.
In the stored gas inflator of the present invention, the initiator increases the stored gas pressure in the small chamber, and the increased pressure ruptures the first burst shim. Therefore, the initiator may have such power capable of increasing the stored gas pressure in the small chamber to the burst pressure of the first burst shim. That is, even a relatively low power initiator can easily rupture the first burst shim.
In the stored gas inflator of the present invention, it is preferable that, in the pressure vessel, the small chamber and the main chamber communicate with each other through a small hole.
According to this structure as mentioned above, the small chamber and the main chamber are always at the same pressure in the normal state before the actuation of the initiator. The second burst shim is subjected to the same pressure from the both sides. Therefore, a member which can be ruptured when subjected to a relatively low gas pressure can be employed as the second burst shim. This can eliminate the need of another process of filling gas into the small chamber besides the process for the main chamber. Filling of gas into both of the small chamber and the main chamber can be achieved by only one filling process, thereby facilitating the assembly of the stored gas inflator.
In one embodiment of the present invention, the gas pressure in the small chamber is increased according to the detonation of the initiator, thereby rupturing both the first burst shim and the second burst shim and thus releasing the gas.
In another embodiment of the present invention, the gas pressure in the small chamber is increased according to the detonation of the initiator, thereby first rupturing the first burst shim and thus releasing gas from the small chamber. Then, the second burst shim is ruptured when the difference between the gas pressure in the small chamber and the gas pressure in the main chamber exceeds the burst pressure of the second burst shim, thereby releasing the gas filled in the main chamber.